Exosomes derived from NGF-overexpressing bone marrow mesenchymal stem cell sheet promote spinal cord injury repair in a mouse model

Cell transplantation has been an appealing way to improve the recovery of motor, sensory, and autonomic functions following spinal cord injury (SCI). Herein, we sought to elucidate the function of bone marrow mesenchymal stem cells (BMSCs) sheet in the progression of SCI and its underlying mechanism. BMSCs were extracted from bone marrow of femur and tibia collected from C57BL/6 mice, and the BMSC sheet was prepared when cells grew to 100% confluence after approximately 14 days. Exosomes (Exos) derived from BMSCs were isolated and characterized. The expression of NGF in the isolated Exos and neural stem cells (NSCs) was quantified. NSCs were co-cultured with Exos derived from the BMSC sheet that was treated with overexpressed NGF (oe-NGF) (Exos-oe-NGF). NSC differentiation, axonal regeneration and locomotor function were detected in vitro and in vivo. The BMSC sheet was successfully prepared and exerted a promoting effect on NSC differentiation into neuronal cells and axonal regeneration after SCI by releasing Exos. Co-culture data showed that NGF was highly expressed in the BMSC sheet-loaded Exos and facilitated neuronal differentiation of NSCs and axonal regeneration. In vivo experimental results unveiled that transplantation of BMSC sheet-loaded Exos-oe-NGF into SCI mice displayed enhanced functional recovery. Collectively, Exo-oe-NGF loaded on the BMSC sheet can accelerate NSC differentiation, axonal regeneration and SCI repair, therefore offering us with a potential therapeutic target for treating SCI.